Interferons are natural proteins with complex biological activity. Most important of their effects are antiviral, cell proliferation inhibitory and immune response enhancing properties.
These effects are utilised in the human therapy. Interferons have therapeutic use in tumour bearing patients.
Such applications are described in the following publications: J. biol. Regul. Homeostatic Agents, 1 pp 93-99 and 177-182, 1987; Intern. J. Cancer, 1987(Suppl.1.), pp 9-13, 1987; J. Interferon Res., Spec. Issue, 1992 April, pp 109-118.
Interferons are also effective in viral infections as it can be seen in the following publications: Lancet, i, p. 128, 1976; Transplantation Proc., 21, pp 2429-2430, 1989; Interferons in the Treatment of Chronic Virus Infections of the Liver, Pennine Press, Macclesfield, 1990.
They have also been proved beneficial in certrain inflammatory diseases: Neurology, 43, pp 655-661, 1993; J. Interferon and Cytokine Res., 15, pp 39-45, 1995.
The high doses applied for reaching a single therapeutic goal, however, may often provoke numerous unnecessary side effects due to the complex actions of these proteins (J. Rheumatol., 20, pp 83-85, 1992; J. Pediatr., 120(3), pp 429-431, 1992; Clin. Exp. Immunol., 90(3), pp 363-367, 1992).
These side effects are quite often dose-limiting factors in the therapeutic use of interferons.
Typically, interferons are applied in combination for therapeutic purposes in order to decrease the severity of side effects. Several different approximations are applicable for combination therapies such as: decrease in the necessary (loses by complementation with drugs of similar mechanism of action (J. Natl. Cancer Inst., 83 pp 1408-1410, 1991); combination with drugs of antagonistic mechanism of action in order to selectively reduce harmful side effects (J. Biol. Resp. Modifiers, 5, pp 447-480, 1986); selective augmentation of the required therapeutic effect by addition of potentiating components or by application of appropriate physical conditions, e.g. hyperthermia (Proc. Soc. Exp. Biol. Med., 169, pp 413, 1982).
It is known from the publications that effective therapeutic application of thimidine-analogous drugs (deoxyuridine derivatives substituted at the 5 position) with antiherpetic action is seriously limited by that fact that a fast viral resistance develops in response to therapeutic concentrations of these drugs. Viral strains resistant to one given drug show crossresistance to other ones with similar chemical structure. Dose reduction of these drugs--if it could be achieved--would reduce the selection pressure on the viruses, thereby reducing, the frequency of the development of resistant mutants and consequently enhancing the therapeutic value of the known antiherpetic agents.